With respect to display devices, one factor that can negatively impact display accuracy is image retention. Image retention, also referred to as image sticking or image persistence, is a well known phenomenon in displays, particularly in LCD displays. Image retention occurs when after a static image is displayed for a certain period of time, subsequent images are affected by the static image such that a low contrast version of the static image remains visible in the new images. Unlike image burn-in, image retention is reversible. Once the static image is removed and new images are displayed, the contrast of the residual static image will gradually decrease until it becomes no longer perceptible by the human eye. The period during which the static image is visible is referred to as the image retention period. Susceptibility of a display to image retention may be influenced by ionic impurities in the liquid crystal and the driving conditions and may increase with the display usage.
When a display is used for applications such as medical diagnostics, the display may not achieve the required accuracy during the image retention period. Several methods have been proposed to quantify the image retention phenomenon. For example, luminance meters may be used to take measurements at different positions on the screen of the display. Because image retention is a time dependent effect, the luminance meters are required to simultaneously obtain data from different points.
Another method for determining image retention involves the use of a charge-coupled device detector and colorimeter to acquire objective image data for later processing and determining an objective measure for image retention. The required equipment is expensive and measurements need to be performed in a controlled environment, making it difficult to determine image retention at a customer's on site location.
One known method to quantify image retention based on visual feedback is to measure the time it takes for the sticking image to disappear. With this method there is still room for subjective errors in judging when the residual image has fully disappeared as well as errors in determining the timing. Also, this method provides no information on how the residual image evolves over time.